automatic KPI for roof pv, generated from external data

[kleins05]

Version 1

• [x] add Gemeindeschlüssel to city data (for unique identification in Marktstammdatenregister)
• [x] add flag show_roof_pv_indicator to enable/disable diagram on city landing page
• [x] add view to read data by Gemeindeschlüssel from Marktstammdatenregister
• [x] display data in frontend using https://apexcharts.com. Will show only past development. No interpolation or target-performance-comparison yet.

Version 2

• [ ] add proper paging when loading external data, see https://github.com/GermanZero-de/localzero-monitoring/pull/395#discussion_r1510007672
• [ ] add labels and units to axes
• [ ] add caching of external data
• [ ] add field roof_pv_target to allow the configuration of a pv target
• [ ] add interpolation of development
• [ ] add target-performance-comparison to the diagram

Version 3

• [ ] create generic data structure for kpis that can be added the same way diagrams can be added already and that can have specific configurations
• [ ] move configuration of pv_target to new data structure
• [ ] (possibly) calculate roof pv potential from external sources like Energieatlas Baden-Württemberg